Review: Specialized S-Works Diverge STR and its Rear Future Shock suspension

Every once in a while a new bike design comes along that challenges the conventions and norms of an industry that is often hesitant to part from the status quo. Some of these stick around and others get consigned to the dustbin of history, to be marched out in retro tech articles and throwback Instagram posts from time to time. (Remember that Bianchi suspension bike for Paris-Roubaix, anyone?)

Specialized’s new S-Works Diverge STR is certainly one of these boundary pushing designs. So the question is: gimmick, or useful innovation that’s here to stay?

After spending some time on the bike, I’m inclined to say it’s the latter.

Also read: The Specialized Diverge STR debuts Rear Future Shock, an innovative approach to gravel suspension

The basics of Rear Future Shock

The headline on the Diverge STR is a new suspension system called Rear Future Shock, a complement to the Front Future Shock system located at the headtube already in place in the Diverge and other Specialized bikes.

Rear Future Shock follows the same basic idea of suspending the rider in place, rather than the bike over the terrain. It builds in a compliant carbon tube, called a Framepost, where the seat tube goes that has 30mm of travel fore and aft. That Framepost acts as a spring that is then controlled by a damper inside the top tube, limiting how quickly the rider moves back and forth. There are nine different Frameposts total, letting riders of weights from 110 to 275 pounds enjoy a properly tuned version of the bike. 

When the rear wheel is pushed up by uneven terrain, the seatpost moves with the same force in the opposite direction of the wheel (the rider is moving backward) to absorb the road chatter. The damper is also tunable with a compression adjustment lever. You can’t completely lockout the damper, but you can significantly reduce the compliance in the system at times when it’s not needed like when riding on fresh tarmac. 

To learn more, check out this full in-depth look at the Diverge STR and Rear Future Shock. 

It takes some time to get used to

Getting started on the Diverge STR, there is definitely a breaking in period of sorts, or more accurately a period of warming up to a new sensation in the bike. 

From the get-go, the saddle sags backward ever so slightly, something I’ve never experienced on a road or gravel bike. This is by design, and Specialized has accounted for this in the geometry of the Diverge STR to keep the fit similar to the Diverge. Regardless, it still feels a little strange.

Choosing the right Framepost is the most time consuming part of the setup experience, and it will likely take some experimenting to get right.

Specialized has studied fit data from riders who have tested this bike and determined the range of rider weights that usually accompany each bike size. The brand has then gone ahead and included the two Frameposts, out of the nine total options, that best fit the majority of riders who use a given frame size.

The experience definitely changes depending on the compliance of the selected Framepost, so it’s going to take a couple rides to both get used to the sensation of Rear Future Shock and find the compliance level that feels right. 

You want it to be active and something you can feel, without it being distracting. At the same time, you don’t want the Framepost so stiff that it may as well not be there. 

I had the 35Nm Framepost installed at first, and found it to be a bit squishy at first. The saddle moving forward and back underneath you is definitely a novel feeling that won’t seem normal until after many miles. But eventually, I began to warm up to it. And by my second ride, I was really glad to have it. 

It wasn’t all pretty in this breaking in period. On descents with the 35Nm Framepost installed, If I hit a sudden bump or riser, I could feel the saddle almost launching me out as the Framepost was suddenly loaded with a lot of energy. With the 43Nm post option, however, I didn’t have this issue, but then I felt the suspension system wasn’t working as much as I would like. 

I ended up being very happy sticking with the 35Nm Framepost and closing the damper halfway on descents.

Once you get things dialed in correctly, the bike provides an enjoyable level of suspension that you can always feel, but not in a distracting way. It melds into the ride experience seamlessly. The compliance makes the ride super smooth from flats to climbs to descents.

If I were to own one, I would play around with another Framepost to be sure I’m using absolutely the right one. If a Diverge STR is in your future, you’ll want to work closely with your shop to make sure everything is the best it can be. 

Still lively despite the suspension

A glaring problem with many gravel suspension systems is that, while they do a good job of taking the bite out of rough roads, they do so at the expense of ride quality. Try to sprint, climb, or otherwise stand out of the saddle for a big effort and the suspension will eat that energy right up.

The Rear Future Shock only works when a rider is seated, so all those watts in a sprint get turned into forward momentum. It’s like having a bike with two polar opposite personalities all in one.

Weight is another factor keeping this bike peppy. A size 56 S-Works version weighs a claimed 8.5kg (18.7lbs). That is about 400 grams more than the previous Diverge without the Rear Future Shock, nothing to scoff at especially when you’re paying more money for the privilege of having a heavier bike. However, the Diverge STR still never feels very heavy on the road. 

Other gravel suspension bikes I have tried have been well north of 9kg (about 20lbs), even reaching the 11kg mark. Those ones you can definitely feel the extra pounds, not to mention the suspension systems when standing out of the saddle. 

Final thoughts

Rear Future Shock has become my favorite gravel suspension I’ve tried so far, though this category is very much in its infancy.

This bike is going to take some getting used to, and it takes an already pricey bike to a new tax bracket — try $14,000 for the S-Works version versus $12,500 for the last one, and $7,500 for the Expert version with SRAM Rival eTap. Does the suspension make the experience $1,500 better? I’m not so sure, and I definitely don’t think it’s necessary to have to enjoy gravel riding. But does the tech work? Certainly. And if you really want gravel suspension, this is the best approach to it I have tried. Anyone who wants more compliance in their gravel bike should give this a look.

Specialized is making the decision somewhat easy for you if you really want a Diverge, though. The high-end models of Diverge will only be available as the STR model with Rear Future Shock going forward, with lower tier models of the previous Diverge (sans Rear Future Shock) occupying lower price points. If you have to have S-Works everything, you’re going to get Rear Future Shock regardless.

Specification

SRAM eTap AXS 1x Red/Eagle group groupset (40T chainring; 10-50T cassette); Roval Terra CLX wheelset; 700×42 Tracer Pro 2BR tires; S-Works Carbon Seat Post;  S-Works Power saddle; S-Works Future Stem; Roval Terra carbon handlebar

Other things to know

Does the Rear Future Shock feel in any way flimsy. Not at all. It feels as well engineered as I would expect of something coming out of Specialized HQ. And Specialized engineers were quick to clarify that the metal “Tendon” connecting the seat tube to the rebound in the top tube, though thin, is stronger than the carbon in the rest of the bike. In other words, it’s not something to worry about breaking. 

Another pain of suspension systems is maintenance. There’s not really anything new to maintain in the Diverge STR because Specialized considers the damper to be a wear item given the relative cost of overhauling it versus replacing it. It can be replaced when it has run the course of its useful life. When that is, I’m not sure. Specialized gives a two-year warranty on it.